An IC card which takes the place of conventional magnetic cards has a terminal for accessing from an equipment side. Since the surface of the terminal requires high resistance to corrosion and hardness for permanent use, an IC card which is subject to two-layered plating of nickel and gold on a copper substrate is generally used.
However, in the general nickel-gold plating, the resistance to corrosion is insufficient. More concretely, there is a problem that pitting corrosion easily occurs on the nickel plating layer due to a pinhole existing on the gold plating layer. On the contrary, countermeasures such that a nickel plating layer and/or a gold plating layer are/is thickened is considered, but there arises a problem of costs and productivity. Therefore, this is not the essential resolution.
The present invention is devised in order to solve the above-mentioned problem of the conventional nickel-gold plating. Namely, its object is to provide nickel-gold plating exhibiting high resistance to corrosion which realizes high resistance to corrosion without sacrificing costs and productivity.